产生声学“冻结波”：在有耗介质中用抗衍射/衰减光束进行模拟实验
Producing acoustic 'Frozen Waves': Simulated experiments with diffraction/attenuation resistant beams, in lossy media
摘要：
所谓的局域波（LW）和“冻结波”（FW），由于其令人惊讶的能量局域化特性，在光学和超声领域引起了极大的关注。LWs抵抗大距离衍射的影响，并且在尺寸小于天线的障碍物之后具有有趣的自我重建（自我修复）特性;而FW（它们的子类）提供了在波传播轴的预定间隔（例如0 < z < L）内任意建模场纵向强度图案的可能性。更具体地，FW是“静止”的局部化场，即，具有静态包络（仅载波在其中传播），并且还可以被赋予高横向局部化。本文通过模拟实验研究了在类水介质中产生频率f_o = 1 MHz的超声FW场的各种情况，并考虑了衰减的影响。我们目前的结果FW的距离L=80 mm，在衰减介质中的吸收系数α在70 <α < 170 dB/m的范围内。这样的模拟FW场构造通过使用我们开发的程序，通过适当的有限叠加的单色超声贝塞尔光束。我们适当注意FW参数的选择，由实验声学所施加的严格限制，以及换能器设计的一些实际意义。冻结波的能量定位特性甚至可以在许多医疗设备中找到应用，例如bistouries或声学镊子，以及用于治疗患病组织（特别是用于破坏肿瘤细胞，而不影响周围组织;此外还用于安全的肾结石关闭等）。
英文摘要：
The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have arisen significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction (self-healing) property, after obstacles with size smaller than the antenna's; while the FWs, a sub-class of theirs, offer the possibility of arbitrarily modeling the field longitudinal intensity pattern inside a prefixed interval, for instance 0 < z < L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate by simulated experiments, various cases of generation of ultrasonic FW fields, with frequency f_o = 1 MHz in a water-like medium, taking account of the effects of attenuation. We present results of FWs for distances up to L=80 mm, in attenuating media with absorption coefficients alpha in the range 70 < alpha < 170 dB/m. Such simulated FW fields are constructed by using a procedure developed by us, via appropriate finite superpositions of monochromatic ultrasonic Bessel beams. We pay due attention to the selection of the FW parameters, constrained by the tight restrictions imposed by experimental Acoustics, and to some practical implications of the transducer design. The energy localization properties of the Frozen Waves can find application even in many medical apparatus, such as bistouries or acoustic tweezers, and for treatment of diseased tissues (in particular, for the destruction of tumor cells, without affecting the surrounding tissues; besides for a safe kidney stone shuttering, etcetera).
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